ATM (Asynchronous Transfer Mode) technology is maturing rapidly for telecommunications as well as computer networking applications. The prospect of an "all ATM" scenario from wide-area network (WAN) to local-area network (LAN) is becoming increasingly promising. Discussions on "ATM to the desktop" have begun to appear in various technical circles, particularly those interested in multimedia applications. Wireless communications, on the other hand, has gained global acceptance and popularity in the cellular voice market. Emerging wireless services such as PCS (Personal Communications Service) are threatening to replace traditional wired telephone and low-rate data access systems. Wireless LAN products (e.g., WaveLan in the Mb/s range) have already found their way in the commercial marketplace. Extending ATM from the LAN/WAN infrastructure towards the wireless user is a task faced by researchers today.
The ATM protocol is intended for transmission on a reliable physical layer such as optical fibers. Wireless links, on the other hand, are notorious for their unreliability and poor bit error rates. Thus, overcoming this incompatibility at the onset is a major research challenge.
Another important aspect of wireless networking is the user mobility. The whole concept of ATM VP/VC (virtual path/virtual circuit) has been centered on fixed point end users Although other research efforts have discussed the use of ATM in wireless networks, they have been limited to centralized architectures 10 with wireless access links as shown in FIG. 1. The centerpiece in FIG. 1 is the ATM switch 12 providing centralized cell routing and mobility management in the entire system. Even though some distributed functions may be assigned to the access points 14, the system intelligence for mobility management resides at the ATM switch 12. The access points are "hardwired" to the central switch while the wireless links serve as extension cords to the users.
It is recognized that wired networks are here to stay, and ATM has the potential to become ubiquitous. In such a case, there will be standard ATM interfaces on workstations, computer servers, and other peripherals attached to a LAN. Therefore, it is advantageous for a wireless LAN to support ATM cell transport directly into the terminals so as to minimize protocol conversion. As exemplified in FIG. 2, the wireless LAN 16 carries "Wireless ATM" (WATM) whereas the WAN 18 carries (standard) ATM, with a WATM/ATM converter 19 (or gateway) in between. An ideal goal for seamless networking would strive for the elimination of the WATM/ATM converter 19. This is unrealistic because wireless link layer protocols need to be designed differently in order to cope with the poor transmission channel characteristics. Furthermore, this idealistic goal is unnecessary because WATM can be designed essentially the same as ATM except for some header byte redefinition and thus keeping the WATM/ATM gateway very simple. It is in this spirit that we approach the subject of Wireless ATM, namely preserving the overall ATM data structure and minimizing changes in the header. Encapsulated ATM and other similar techniques are deemed consistent with this philosophy and are part of the consideration.